The primary objective of this proposal is to establish and characterize mechanisms for regulation of protein synthesis at the translational level. The study will utilize a highly efficient fractionated cell-free protein system derived from mammalian cells and will focus on two probable sites of regulation - mRNA structure and mRNA-ribosome-initiation factor interaction. Competitive translation experiments will be used to establish: (1) whether different mRNAs (cellular and viral) are translated with different efficiencies, (2) whether translation components and/or conditions effect alterations in the relative efficiency of mRNA translation, and (3) the stage of translation involved in differential efficiency of translation. The specific inhibition of mRNA translation by complementary DNA (cDNA) will be used to determine which regions of mRNA contribute toward efficiency of translation and the extent to which these regions differ in different mRNAs. A Chinese Hamster Ovary (CHO) cell line which appears to have an alteration in regulation of translation of viral mRNA will be investigated to determine whether the basis for this alteration resides in a translation component.